A switching power supply of a PWM (Pulse Width Modulation) driving type generally includes, as circuit elements forming a voltage feedback loop, an error amplifier for generating an error signal corresponding to a difference between an output voltage or a corresponding feedback voltage and a predetermined reference voltage, a slope oscillation part for generating a triangular or sawtooth-waved slope voltage, and a comparator for comparing the error voltage and the slope voltage to determine an ON timing of an output transistor.
In many cases, a switching power supply employing a current mode control system having a current feedback loop in addition to the voltage feedback loop is employed for applications requiring high load response characteristics. In the switching power supply of the current mode control system, in general, the voltage feedback loop and the current feedback loop are formed to generate the slope voltage by adding a first slope voltage having a constant slope and a second slope voltage having a slope depending on a load current.
However, in the conventional switching power supply, the slope of the first slope voltage is fixed to a constant value. In addition, the slope of the second slope voltage is set to a multiplication of the load current with a constant current feedback gain.
However, a slope of the first slope voltage and a slope of the second slope voltage (the current feedback gain) providing the best responsiveness and stability of the switching power supply are varied depending on the usage situations (e.g., an input voltage, an output voltage, a switching frequency, a load current, a temperature and the like) of the switching power supply.
Therefore, it is difficult for the conventional switching power supply to optimize its responsiveness and stability depending on its usage situations.